• Title/Summary/Keyword: 탄성 특성

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Numerical Analysis of NDT Using Elastic Stress Waves in Concrete Lining (터널 라이닝내부에서 전파되는 탄성응력파를 이용한 수치해석적 비파괴검사)

  • 김문겸;이재영
    • Computational Structural Engineering
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    • v.11 no.3
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    • pp.187-198
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    • 1998
  • 지하구조물의 건전성을 평가하기 위한 비파괴시험으로써 탄성응력파를 이용한 충격반향탐사법을 수치해석적인 방법을 통하여 수행하였다. 즉, 일면만으로 접근 가능한 터널 면에서의 충격가진과 동적응답의 측정으로 이질면을 포함한 내부의 상태를 예측할 수 있다. 연구의 수행은 탄성거동을 하는 매질 내부에서 전파되는 탄성응력파의 특성을 이해하고, 이를 동적 유한요소해석으로 모형화하여 충격반향탐사법을 수치해석적으로 수행한다. 이질재료가 2개의 층을 이루고 있는 경우 표면층의 두께를 쉽게 측정할 수 있었으며, 구조물의 병진운동, 휨운동과 구조물 내에서 다중반사되는 탄성응력파에 의한 복합적인 영향을 받는 터널과 같은 원통형 구조물에서 동적응답의 주파수 특성으로부터 터널라이닝 내부에 형성된 공동의 위치와 크기의 예측이 가능하였다. 수치해석적인 방법과 병행하여 다양한 형태의 경계조건을 가지는 구조물에 대한 충격반향탐사법의 실험을 수행할 경우 실제적인 문제에 적용, 건전성 평가의 지표를 마련할 수 있을 것으로 사료된다.

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Study on Skin Elasticity Property between Face and Forearm according to the Environmental Change of Stratum Corneum (각질층 환경변화에 따른 얼굴과 하박내측 피부의 탄력 특성 비교연구)

  • Chang, Minyoul
    • Journal of the Society of Cosmetic Scientists of Korea
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    • v.44 no.4
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    • pp.455-463
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    • 2018
  • Skin elasticity has been known to be influenced by the change of dermal components such as collagen, elastic fiber, and glycosaminoglycans. However, it is unclear whether the uppermost epidermis may affect the mechanical characteristics of elasticity. In present study we tried to find the role of stratum corneum when determining the elastic property under skin bioengineering measurement with $Cutometer^{(R)}$. A total of 10 healthy volunteers aged 25-40 years were investigated by the parameters reflecting the skin elasticity from face and volar forearm. Within various ranges of suction pressure, R0 (=Uf), R7 (=Ur/Uf) and R8 (=Ua) were obtained to explore the depth-associated elasticity. In addition, these parameters were re-measured after the skin was fully hydrated. As results, we found that the measurement of depth-associated elasticity was possible as using various suction pressure. And the R7 parameter was significantly lower from face than those from forearm in before hydration (p < 0.05). Also, we found that the hydration of stratum corneum could affect skin elasticity. Especially, the R7 parameter at 300 mbar suction pressure of face skin showed significantly increased values than that of before hydration (p < 0.05). Interestingly, measured data from the face before and after hydration manifested relatively higher variation than from the forearm. These results suggest that it is possible to evaluate the skin elasticity considering the changes of stratum corneum and epidermis by using various suction pressure and skin hydration.

A Study on Impact Sound Insulation Properties of EPDM Micro Cellular Pad (에틸렌-프로필렌-디엔 삼원 공중합 (EPDM) 발포체의 충격음 저감 특성에 관한 연구)

  • Lee, Kyung-Won;Lee, Jung-Hee;Sohn, Ho-Soung
    • Elastomers and Composites
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    • v.35 no.2
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    • pp.138-148
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    • 2000
  • In order to investigate the possibility of EPDM micro cellular pad (MCP) as an impact sound insulation product, we studied static/dynamic properties and vibration transfer characteristics of EPDM MCP depending on shape, thickness, degrees of foaming by using material test system (MTS) and lab scale mock-up test apparatus. Static/dynamic rigidity is increased when shape is simple. thickness and degrees of foaming low. We could see that dynamic stiffness is proportional to the transmissibility of EPDM MCP. When dynamic stiffness is increased, characteristic peak at transmissibility curve moves high frequency range or snows increase of maximum value of transmissibility. For lab scale mock-up test and finite element method, EPDM MCP shows low vibration velocity and superior mode shape to just concrete plus slab structure. We could confirm that possibility of EPDM MCP as a impact sound insulation product is high.

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Dynamic Responses on Semi-Infinite Space Due to Transient Line Source in Orthotropic Media (선형하중에 의한 직교이방성 매체의 반구계에서 동적 응답 특성)

    • Journal of KSNVE
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    • v.8 no.5
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    • pp.974-980
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    • 1998
  • The analysis of dynamic responses are carried out on several orthotropic systems due to transient line source. These include infinite and semi-infinite spaces. The media possess orthotropic or higher symmetry. The lode is in the form of a normal stress acting with parallel to symmetry axis on the plane of symmetry within the materials. The results are first derived for responses of infinite media due to a harmonic line source. Subsequently the results for semi-infinite are derived by using superposition of the solution in the infinite medium together with a scattered solution from the boundaries. The sum of both solutions has to satisfy stress free boundary conditions thereby leading to the complete solutions. Explicit splutions for the displacements due to transient line loads are then obtaind by using Cargniard-DeHoop contour.

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Elastic properties of ion-assisted Cr films measured by brillouin light scattering (브릴루앙 산란 실험을 이용한 이온빔 보조 증착법의 Cr 박막의 탄성특성)

  • ;;;John R. Dutcher
    • Korean Journal of Optics and Photonics
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    • v.6 no.1
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    • pp.50-55
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    • 1995
  • We have performed Brillouin light scattering experiments to study the elastic properties of Cr films deposited on soda-lime glasses by using Ar-ion assisted deposition techniques. The elastic constants of the films increased as the ion-current density employed during the film deposition increases and they approached to the values of bulk Cr. The best fit values of the elastic constants of the films manufactured with ion current density of $400\muA/cm^{2}$are $c_{11}=296, c_{13}=83, c_{33}=289$, and $c_{55}=c_{44}=108(\times10^9/N/m^{2}}$ and these are 5% lower than those of bulk Cr in hexagonal symmetry. metry.

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Variation in Characteristics of Elastic Waves in Frozen Soils According to Degree of Saturation (포화도에 따른 동결토의 탄성파 특성 변화)

  • Park, Jung-Hee;Kang, Min-Gu;Lee, Jong-Sub
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.33 no.3
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    • pp.1063-1075
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    • 2013
  • The strength of frozen soils is one of the significant design parameters for the construction in frozen ground. The properties of frozen soils should be investigated to understand the strength of frozen soils. The objective of this study is to figure out the characteristics of elastic waves in frozen soils, which reflect the constituent and physical structure of frozen soils in order to provide fundamental information of those according to the degree of saturation. Freezing cell is manufactured to freeze specimens, which are prepared with the degree of saturation of 10%, 40%, and 100%. Piezo disk elements are used as the compressional wave transducers and Bender elements are used as the shear wave transducers. While the temperature of specimens changes from $20^{\circ}C$ to $-10^{\circ}C$, the velocities, resonant frequencies and amplitudes of the compressional and shear waves are investigated based on the elastic wave signatures. Experimental results reveal that the elastic wave velocities increase as the degree of saturation increases. The variation of resonant frequencies coincide with that of elastic wave velocities. A marked discrepancy in amplitudes of compressional and shear waves are observed at the temperature of $0^{\circ}C$. This study renders the basic information of elastic waves in frozen soils according the degree of saturation.

A Study on the Elastic Wave Velocity of Magnetostrictive Materials (자왜 재료의 탄성파 속도에 관한 연구)

  • 강국진;노용래
    • The Journal of the Acoustical Society of Korea
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    • v.20 no.4
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    • pp.54-61
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    • 2001
  • Magnetostrictive materials have nonlinear elasto-magnetic properties. However the constitutive equations to describe the nonlinear properties are not available, yet. In this study we develope the equation in magnetostrictive materials by use of piezomagnetic constitutive equation which is quasi-linearized. With the wave equation, we determine the propagation velocity inside the magnetostrictive materials when a plane wave propagates along a given magnetic field. Validity of the calculated velocity is verified through comparison with experimental velocity measurement results for the most representative magnetostrictive materials. Terfenol-D.

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Experimental and Numerical Analysis for Superelastic Behaviors of SMAs with Strain-rate Dependence (변형률 속도에 따른 형상기억합금 초탄성 거동의 실험 및 해석 연구)

  • Roh, Jin-Ho;Park, Jeong-In;Lee, Soo-Yong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.1
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    • pp.9-15
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    • 2011
  • The influence of the strain-rate on the superelastic behaviors of shape memory alloys (SMAs) wires is experimentally and numerically investigated. The one-dimensional SMA constitutive equations considering strain-rate effect is developed. The evolution of stress-strain curves of SMA wires is examined with various strain-rates. Results show that the superelastic behaviors of SMAs may significantly be changed depending on the variation of strain-rate.

Prediction of Tensile Properties for Short-fiber-reinforced Composites (단섬유 보강 복합재료의 기계적 특성 평가에 관한 연구)

  • Jeong, Tae-Heon;Lee, Dong-Joo
    • Journal of the Korean Society of Industry Convergence
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    • v.3 no.1
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    • pp.53-59
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    • 2000
  • 단섬유 보강 복합재료의 종횡비(aspect ratio)를 변화시키며 기계적 특성(탄성계수, 인장강도)을 평가하였다. 2차원 다중 파이버(multi-fiber) 모델을 이용하여 엇갈린(staggered) 배열과 규칙적(aligned) 배열에 대해 유한요소 해석을 하였다. 단섬유 복합재료의 유효탄성계수 및 인장강도는 섬유와 기지의 탄성계수비, 섬유 배열상태, 그리고 단섬유 종횡비의 함수로 표현되었으며, 해석결과의 탄성계수와 인장강도는 이론 모델의 결과와 사출 성형된 PEEK 복합재료 시험편의 결과와 비교하였다. 시험결과는 낮은 종횡비에서 이론 모델 결과와 일치함을 보였다. 단섬유 보강 복합재료의 배열 및 종횡비 변화에 따른 섬유보강 효과에 따른 계면응력 상태는 기계적 특성 결정에 중요한 영향을 보였다.

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Surface acoustic wave characteristics of $Pb(Sn_{1/2}Sb_{1/2})O_3-PbZrO_3-PbTiO_3$ ceramics ($Pb(Sn_{1/2}Sb_{1/2})O_3-PbZrO_3-PbTiO_3$ 세라믹스의 탄성 표면파 특성)

  • 홍재일;김준한;유주현;강진규;위규진;박창엽
    • Electrical & Electronic Materials
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    • v.4 no.3
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    • pp.220-228
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    • 1991
  • 본 연구에서는 핫프레스법으로 제작된 0.05Pb(Sn$_{1}$2/Sb$_{1}$2/)O$_{3}$-0.60PbZrO$_{3}$-0.35PbTiO$_{3}$+x[wt%]MnO$_{2}$ 세라믹스에 대해 구조적, 전기적 특성 및 탄성 표면파 특성을 조사하였다. x가 0.4인 조성을 1150[.deg.C]에서 45분간 소성한 시편의 경우 탄성표명파의 전기 기계 결합 계수 k$_{s}$ $^{2}$가 2.8[%], 기계적 품질 계수 Q$_{m}$ 이 1976으로 탄성 표면파 소자용 기판으로서 응용 가능함을 보였다.

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